The goal of this program project is to fully characterize dental hard tissues, provide important information on their biomechanics and mineralization, and modify them to enhance adhesion of polymer based adhesives of them. This revised proposal is for years 11-15 of a program project grant, Characterization and Modification of Dental Hard Tissues. For ten years new information has been generated about the nature of the dentin substrate for preventive and restorative dentistry, including its structure, mechanical and etching properties, and its interface with polymeric dentin adhesives. In this proposed period the substrate will be expanded to include other forms of dentin, as well as enamel and cementum. The program project has a Laboratory, Statistical and Administrative Core and 4 projects: Structure/Properties of Altered Forms of Dentin and Cementum; Biomechanics of Dentin; The Bonding Zone with Dental Calcified Tissues; and Tools for Tissue Engineering Tooth Structure. The Core will coordinate all projects administratively, collect teeth and provide specimens for all experiments on all projects, manage the data base, conduct statistical analyses and insure that the results are disseminated. Project 8 will identify key materials structure/properties relationships that allow quantitative and unique identification of a broad array of various forms of dentin, its alterations due to age, disease processes and treatment and cementum. The new knowledge will serve as a foundation for improved understanding of these tissues and their variations as well as provide insights into dental calcified tissues that will be useful to advancing concepts is tissue engineering. The information also will be used to model mechanical properties of the tooth, including its fundamental elastic constants and factors contributing to fracture resistance and failure in one project. These models will be made on 3 length scales, from the constituent to the continuum. Thus projects 8 and 9 are complementary to each other in understanding dental calcified tissues. Project 10 will use the information from projects 8 and 9 to develop novel substrate morphologies and properties that will enhance the durability of bonds to resin based composites. Project 11 will use the same methods as the other projects to evaluate transgenic mouse models for tissue engineering of teeth. It will focus on the analysis of dentin and cementum in the mouse model, and be used as a tool to determine the role of TGF-Beta on the development and repair of these tissues.